删除和析构函数(C ++)的一个有趣案例

我有一段代码，可以多次调用析构函数，并访问成员函数，即使在保留成员变量值的情况下调用析构函数也是如此.调用delete之后，我仍然可以访问成员函数，但是成员变量为空(全部为0).而且我不能将delete加倍.请对此进行解释.

I have a piece of code where I can call the destructor multiple times and access member functions even the destructor was called with member variables' values preserved. I was still able to access member functions after I called delete but the member variables were nullified (all to 0). And I can't double delete. Please kindly explain this.

#include <iostream>
using namespace std;

template <typename T>
void destroy(T* ptr)
{
    ptr->~T();
}

class Testing
{
public:
    Testing() : test(20)
    {

    }

    ~Testing()
    {
        printf("Testing is being killed!\n");
    }

    int getTest() const
    {
        return test;
    }

private:
    int test;
};

int main()
{
    Testing *t = new Testing();
    cout << "t->getTest() = " << t->getTest() << endl;

    destroy(t);
    cout << "t->getTest() = " << t->getTest() << endl;

    t->~Testing();
    cout << "t->getTest() = " << t->getTest() << endl;

    delete t;
    cout << "t->getTest() = " << t->getTest() << endl;

    destroy(t);
    cout << "t->getTest() = " << t->getTest() << endl;

    t->~Testing();
    cout << "t->getTest() = " << t->getTest() << endl;

    //delete t; // <======== Don't do it! Double free/delete!
    cout << "t->getTest() = " << t->getTest() << endl;

    return 0;
}